Sensors are used in many aspects of modern life, from driving a car to getting water from a tap. In a car, for example, sensors may measure the pressure in a fuel rail, the temperature of engine coolant, the oxygen content of exhaust gases, etc. The most common type of sensor is a bridge-type transducer. Bridge-type transducers require an input voltage which is often a constant DC voltage of some known value. For accurate measurement, the input voltage must be as consistent as possible so that it may be factored out of the resulting sensor reading. Unfortunately, the use of such DC input voltages is susceptible to factors including the drift of the sensor components (due to factors such as, for example, temperature) and noise.
The impact of these negative factors may be significantly reduced by the use of an AC input voltage. But the use of AC signals may introduce additional complexities. For example, if the AC signal originates in a computer, a digital-to-analog (D/A) converter must be used in order for the sensor to receive an analog input signal. Additionally, an analog-to-digital (A/D) converter may be used to re-digitize the signal after measurement, for example, to record the data within a computer. Such components as the D/A and A/D convertors generally effect the signal by inducing gains (changes in amplitude). Since sensors generally are read by determining the gain induced by the sensor, additional gains, caused by other components or signal processes, will affect the precision and confidence in any measurements determined from the total gain of the system. Therefore, in order to achieve precise measurements, any additional gains should be factored out (or at least minimized).
Past methods of minimizing these additional gains typically involve calibrating the system through careful measurement of the additional gains caused by the non-sensor components and adjusting the output to compensate for these measured values. This is burdensome, however. Since the gain of a component may change over time, an operator may be required to regularly calibrate the system. This greatly increases the time and cost required to make accurate measurements, as well as requiring high stability A/D and D/A components. Therefore, there is a need for a method of reducing the impact of non-sensor components on sensor measurements without the burdensome efforts required of regularly measuring and compensating for such non-sensor components.